1. Field of the Invention
This invention relates to methods and apparatus for the controlled degassing of closed and sealed containers of liquid such as beverages, waste water and activated sludge using precision ultrasonics, sparging or stirring. The invention also relates to methods and apparatus for controlling the amount of headspace in a container of liquid.
2. Description of the Background
Ultrasonics has been used in the beverage industry for many years as one of the techniques for degassing containers to measure the level of carbon dioxide (CO.sub.2) or nitrogen (N.sub.2) in beverages such as soft drinks, beer and carbonated alcoholic products. However, ultrasonics has had only limited acceptance as an accurate method for determining the level of gases in a beverage. For the most part, these gases are artificially introduced into the beverage as part of the production process although some trace amount may be present from the atmosphere. Ultrasonics agitation is also suitable for measuring small amounts of oxygen (O.sub.2) that may unavoidably enter the beverage during the production process.
The degassing process, especially the rate of degassing, is dependent on the ultrasonic power density at the beverage. Standard ultrasonics, available to the beverage industry, have not been developed as precision instruments for degassing to determine gas content. This lack of precision limited the use of ultrasonics for determining the quantities of various beverage gasses (CO.sub.2, O.sub.2, N.sub.2).
The problem in any ultrasonic technique, where repeatability is an issue, is to use a device where the power density at the drink is held constant at the beverage for any test at any time. Most electronic ultrasonic devices use resonance circuits tuned to a particular ultrasonic frequency in the 20K Hz to 50K Hz range. However, the strength of the resonance and hence the strength of the ultrasonic waves that are produced are affected by the loading from every element in the electro-mechanical configuration. This includes (i) the beverage container size, (ii) the material of the container and its contents, (iii) the water level in the ultrasonic tank, (iv) the impedance of the electronic circuit, (v) the geometry of the ultrasonic tank, (vi) the temperature and density of the liquid in the ultrasonic tank and beverage container, (vii) other mechanical parts inserted into the ultrasonic tank such as hangers and supports for the beverage container, and (viii) variations in AC line power.